1. Field of the Invention
This invention relates particularly to the preparation of orthosilicic acid tetraesters of monoalkyl ethers of an aliphatic glycol, particularly to orthosilicic acid tetraalkoxyalkyl esters having 2 to 6 carbon atoms in the main chain and 1 to 4 carbon atoms in the chain of the monoalkyl ether. This invention is particularly directed to a process for the production of such orthosilicic acid tetraalkoxyalkyl esters which can be carried out at an exceptionally high volume-time yield, such as a volume-time yield equal to or better than the volume-time yields obtained in the preparation of orthosilicic acid tetraalkyl esters from simple alcohols.
2. Discussion of the Prior Art
It is known to prepare orthosilicic acid tetraalkylesters by the reaction of silicon, iron silicide or ferrosilicon with alcohol in the presence of the corresponding alcoholate which process is carried out in the presence of 70 to 99 weight percent of the corresponding orthosilicic acid tetraalkyl ester. The process is carried out such that the alcohol which forms such ester on reaction with the silicon containing compound is continuously added to the reaction mixture. The process provides good volume-time yields principally in the production of lower alkyl orthosilicic acid tetraalkyl esters. However, when the alkyl radical of the ester grouping becomes long the volume-time yield obtained by the process becomes considerably poor.
It is known in this reaction to utilize silicon of specific grain sizes as these grain sizes are known to effect the speed of formation of the ester. The reaction speed is improved when the silicon has a good ability to become wetted by the alcohol or alcoholates used in the process. In contrast to this, it is known that ether alcohols can be used as stabilizing agents for chlorinated hydrocarbons whereby the chlorinated hydrocarbon is stabilized against attack by a metal. It is also known that the surface of light metals is passivated when contacted with an ether alcohol. It has, therefore, been expected that the preparation of an orthosilicic acid tetraalkoxyalkyl ester from silicon, ferrosilicon or iron silicide using an ether alcohol would proceed quite poorly owing to the inability of the silicon to be adequately wetted by the ether alcohol. It was expected that the formation of any tetraalkoxyalkyl ether of orthosilicic acid would be obtained quite slowly.
For these reasons orthosilicic acid esters of ether alcohols have, in practice, been prepared by the transesterification of orthosilicic acid methyl esters with the corresponding ether alcohol. This process is complicated owing to the fact that a two-step process must be performed. Moreover, the process does not provide the desired high volumne-time yields such as are obtained in the preparation of orthosilicic acid tetra (lower alkyl) esters.
It, therefore, became desirable to provide a process for the preparation of such tetraalkoxyalkyl esters of orthosilicic acid whereby the desired ester could be obtained in a high volume-time yield. It became particularly desirable to provide such a process which could be carried out in one step. Moreover, it became desirable to provide such a process which could be carried out using readily available materials and did not require the assembly of an elaborate reaction vessel or system or the imposition of expensive processing parameters.